The present invention relates to particulate filters for diesel exhaust systems. More particularly, the present invention relates to particulate filter assemblies that can be incorporated into diesel exhaust treatment devices.
Because regulatory agencies have recently mandated the reduction of particulate emissions in diesel engines, there has been increased activity in the development of diesel particulate filters, that is, exhaust emission filters for diesel engines. The role of a typical diesel particulate filter is to trap and remove the particulate components of the diesel exhaust stream, which include diesel soot and aerosols such as ash particulates, metallic abrasion particles, sulfates, and silicates, to prevent their discharge from the tailpipe.
Diesel particulate filters should provide long-term operation without diminishing the filtration efficiency of the filter and performance of the engine. Factors related to the performance of diesel particulate filters include but are not limited to high temperatures (e.g., up to 1400° C.), capability to store soot and ash, pressure loss, low thermal mass, stability, and durability. In addition, manufacturing costs and assembly volume are important considerations.
The filtration is achieved by a porous structure (e.g., filter media) that allows transmission of the fluid phase but stops or captures diesel particulate matter larger than a threshold particle size. Variations in the thermal characteristics of the frame and media materials of the diesel particulate filter has often run into problems of cracking. This is largely due to the thermal mismatch of the center tube and the casting materials as well as the low strength of both materials. This has been observed in diesel particulate filters that are formed by a co-casting process. Accordingly, it is desirable to provide a crack-free assembly for the diesel particulate filter.